This invention relates to radiation-curable, silicon-containing resin compositions that can be used to fabricate films. These films can be used, for example, as dielectric films in semiconductor devices. The invention also relates to methods for curing these compositions and for using these compositions for forming patterns.
It is well known in silicon chemistry and the silicone industry that the hydroxyl group (e.g., water, alcohol, silanol, etc.) will react with a hydrogen atom bonded directly to silicon to produce a hydrogen molecule and the silicon-oxygen bond, i.e., Si--O (refer to Chemistry and Technology of Silicones, 2nd Edition, p. 90, Walter Noll, Academic Press, Inc. (London) Ltd., 1968; Organosilicon Compounds, p. 200, C. Eaborn, Butterworths Scientific Publications (London), 1960). Although the uncatalyzed reaction will run at elevated temperatures, it is widely known that this reaction will run more readily in the presence of a transition metal catalyst such as platinum, palladium, etc., or in the presence of a basic catalyst such as an alkali metal hydroxide, amine, etc., or in the presence of a Lewis acid catalyst such as a tin compound, etc. Moreover, the reaction between Si-H and SiOH has been proposed as a room-temperature curing mechanism for silicones (Chemistry and Technology of Silicones, p. 205, p. 397).
Radiation-mediated resin curing reactions are also known in the art. Refer, for example, to Tsugio Yamaoka and Hiroshi Morita, Photosensitive Resins, published by Kyoritsu Shuppan, 1988; Encyclopedia of Polymer Science and Engineering, Volume 9, pp. 97-138; Lithographic Resists, Wiley-Interscience (New York), 1985; and Saburo Nonogaki, Microprocessing and Resists, published by Kyoritsu Shuppan, 1987, and so forth.
Radiation-mediated resin curing can proceed, for example, through a crosslinking reaction or through a polymerization reaction. The crosslinking reaction is exemplified by the photodimerization of cinnamic acid compounds; the reaction between the mercapto group and an olefin; and reactions based on photosensitive groups such as the diazo group or azide group.
The polymerization reaction approach is exemplified by the combination of a functional group such as the acryloyl or methacryloyl group with a polymerization initiator that generates radicals upon irradiation and cationic polymerization of the epoxy group, lactone, active vinyl group, etc., based on the radiation-induced generation of a cationic polymerization initiator.
Curing methods are also available in which the crosslinking or polymerization reaction is induced through the catalytic activity of an acid which is generated by a substance upon exposure to radiation (hereinafter abbreviated as an acid generator). The acid generators used in these methods include aryldiazonium salts, diaryliodonium salts, triarylsulfonium salts, triarylselenonium salts, dialkylphenacylsulfonium salts, dialkyl-4-hydroxyphenylsulfonium salts, sulfonate esters, iron-arene compounds, silanol-aluminum complexes, and so forth.
Specific examples of curing using acid generators include the curing of epoxy resins through the radiation-induced generation of a Lewis acid such as boron trifluoride (S. I. Schlesinger, Polym. Eng. Sci., 14, 513 (1974); G. Smets, A. Aerts, and J. Van Erum, Polym. J., 12, 539 (1980)); the fabrication of silicic acid glass thin films from the combination of a special siloxane and an acid generator (Japanese Patent Application Laid Open Kokai or Unexamined! Number Hei 6-80879 80,879/1994!; Jpn. J. Appl. Phys., Volume 32(1993), pp. 6052-6058); and photocuring technologies for epoxy resins that use aluminum compounds and ortho-nitrobenzoyloxy silicon compounds (S. Hayase, T. Ito, S. Suzuki, and M. Wada, J. Polym. Chem. Ed., 20, 3155 (1982); ibid, 19, 2185 (1981); S. Hayase, Y. Onishi, S. Suzuki, and M. Wada, Macromolecules, 18, 1799 (1985); and Japanese Patent Application Laid Open Kokai or Unexamined! Number Sho 58-174418 174,418/1983!).
Curing reactions that use a substance which evolves base upon exposure to radiation (hereinafter abbreviated as a base generator) are also being investigated. The base generators used in this technology include organic and inorganic nitrogenous compounds that, upon irradiation, produce organic amine, ammonia, or quaternary ammonium hydroxide. Examples of such compounds include ortho-nitrobenzyl benzylcarbamate compounds (M. R. Winkle and K. A. Graziano, J. Photopolym. Sci. Technol., 1990, 3, 419; J. F. Cameron and J. M. Frechet, J. Am. Chem. Soc., 1991, 113, 4303; J. M. Frechet and J. F. Cameron, Polym. Mater. Sci. Eng., 64, 55(1991)); metal-ammine complexes (for example, S. K. Weit, C. Kutal, and R. D. Allen, Chem. Mater., 4, 453-457 (1992)); and 4-(ortho-nitrophenyl)dihydropyridines (DE Patentschrift 1,923,990). Curing using base generators is specifically exemplified by the radiogenerated base-catalyzed cure of compositions comprising phenolic resin plus epoxy crosslinker plus melamine curing agent (EP 0555749 A1; J. M. Frechet and J. F. Cameron, Polym. Mater. Sci. Eng., 64, 55 (1991); C. Kutal and C. G. Wilson, J. Electrochem. Soc., 134, 2280-2285 (1987)) and the radiogenerated base-catalyzed cure of poly(silsesquioxane) alone or in combination with tetraphenoxysilane (Japanese Patent Application Laid Open Kokai or Unexamined! Number Hei 6-148887 148,887/1994!).
The cured regions produced by crosslinking in these methods are generally much less solvent-soluble than the uncured regions. This property can be utilized for imaging and patterning applications.
The above curing systems have several deficiencies. For instance, curing systems that use the photodimerization of cinnamic acid compounds, curing systems in which the photosensitive group is the diazo or azide group, curing systems that utilize the addition of mercaptan across olefin, and curing systems based on the polymerization of such functional groups as the acryloyl group, methacryloyl group are generally not thermally stable. As such, these types of systems do not yield a cured product that can withstand use or processing at high temperatures.
Likewise, curing reactions using the dimerization of cinnamic acid compounds and the reactions mediated by radicals generated from the diazo or azide group are equivalent reactions with regard to the photoreaction, i.e., no amplification effect is present. These systems are, therefore, not suited for curing with low-intensity (i.e., low numbers of photons) radiation.
Similarly, curing systems based on the addition of mercaptan across olefin result in an undesirable odor and corrosivity. Additionally, curing systems based on the radical polymerization of functional groups such as acryloyl, methacryloyl, etc. can be inhibited by air (oxygen).
Curing systems that utilize photogenerated acid offer a number of advantages such as (1) an amplification effect even with low-intensity radiation because the generated acid functions as a catalyst of the crosslinking reaction, and (2) the cure systems are not inhibited by oxygen. However, this curing system also has drawbacks such as (1) the tendency of the acid to corrode base materials and (2) problems with the electrical properties of the cured material due to the presence of ionic residues.
Curing systems that utilize photogenerated acid are also limited to materials capable of acid-catalyzed polymerization, i.e., generally to the epoxy group, acrylic group, and the like. One exception, however, is the report of the fabrication of silicic acid glass thin films through the combination of a special siloxane and an acid generator (Japanese Patent Application Laid Open Kokai or Unexamined! Number Hei 6-80879; Jpn. J. Appl. Phys., Volume 32(1993), pp. 6052-6058). The method described in this reference, however, requires an extremely specialized polysiloxane. Moreover, the reaction results in a large weight loss causing pinholing, cracking, etc. which are fatal for application such as protective coatings, dielectric coatings, or planarizing coatings.
Base generator curing technology offers the same advantages as acid generator curing technology, i.e., (1) it provides an amplification effect for the crosslinking reaction, even with low-intensity radiation, because the generated base again functions as a catalyst of the crosslinking reaction, (2) oxygen does not inhibit the cure and (3) substrate corrosion is a less significant problem than with acid generator technology.
The present invention is directed to solving the problems described above. It introduces (a) radiation-curable compositions that undergo very little cure-associated weight loss, can be cured by low-intensity radiation, and provide a heat-resistant cured product; (b) methods for curing the aforesaid radiation-curable compositions; and (c) a method of forming patterns that utilizes the aforesaid compositions and curing methods.